Hi Daan,
From what I remember of a failure analysis, larger chip caps are the most
susceptible, and the damage is usually not observable from the component
exterior, nor is it testable for screening. The failure occurs during
powered operation over time as metalization progresses along internal
fractures of the layers changing the component value. Seems to me I recall
a more conservative limit of 4 degrees C per second with some of the chip
caps. Recommend that the component supplier be considered. Some are more
susceptible than others.
Best regards,
Mel Parrish
Director, Training Materials and Resources
Soldering Technology International Inc.
102 Tribble Drive
Madison, AL 35758
256 705 5530
256 461 9566 Fax
[log in to unmask]
www.solderingtech.com
-----Original Message-----
From: TechNet [mailto:[log in to unmask]]On Behalf Of d. terstegge
Sent: Thursday, September 04, 2003 10:33 AM
To: [log in to unmask]
Subject: [TN] Preheat of ceramic chip capacitors
Hi Technet,
I just saw a specification for the soldering profile for a simple
0805-sized ceramic chipcapacitor. It mentions a maximum preheat ramp,
both for wave and for reflow soldering, of 2 degrees Celcius per second.
In the beginning of the slope, for some of our products, we go slightly
higher than this.
One of our customers now thinks that the preheat ramp being steeper
than the component suppliers specification must be the reason for
malfunctioning of this specific part.
I won't annoy you with all the discussions we had and the
investigations that we've done, I just hope to get an answer to the
following question: is it possible that a preheat ramp of 3 °C/s results
in failures (but without any visible damage) of 0805 ceramic
chipcapacitors ?
Best regards,
Daan Terstegge
Thales Communications
Unclassified mail
Personal Website: http://www.smtinfo.net
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